Multi-chip RF modules, such as transceivers, frequency multipliers, up-converters and down converters, have been designed and built for decades. The most common method used by manufacturers of multi-chip RF modules, is to assemble the chips and RF components in a machined metal housing with expensive waveguide or coaxial interfaces. A Typical high frequency module consists of a number of Microwave Monolithic Integrated Circuit (MMIC) chips, substrates with matched impedance lines and filters, and passive components, all mounted with epoxy or solder to a machined housing. The chips and substrates components are typically connected to other each other via wire or ribbon bonds. Tuning of the radio frequency modules after assembly is almost always necessary.
High frequency modules typically require special RF board material or substrate with stable dielectric characteristics and tight manufacturing tolerances because of the inherent shorter wavelength. They also require intricate housing enclosures with channelization for wave propagation and isolated compartments to avoid interference and prevent oscillations. These housings are typically made of expensive coefficient of thermal expansion (CTE) matched material to prevent damage to the semi-conductor chips during temperature cycles.
The miniature RF module of the current invention is highly integrated, uses no metal housings, has a small foot print, provides high level of isolation between the different circuits, and costs a fraction of prior art multi-chip modules. The miniature RF module simply consists of a base board, a number of semiconductor chips and a cover made of laminate material. The base board provides 3 main functions: 1) acts as a carrier for the chips, 2) provides all the necessary matched impedance lines and filters (etched on it), and 3) provides an interface for easy mounting of the miniature module using surface mount technology (SMT). The semi conductor chips used in the miniature module can be SMT type (packaged dies) or MMIC bare dies. The cover is made of machined printed circuit board (PCB) material, such as FR-4. FR-4, which is an abbreviation for Flame Retardant 4, is a laminate consisting of a continuous filament glass cloth material with an epoxy resin binder. Although different types of PCB materials may be used, FR-4 is preferred due to several mechanical and electrical properties; including high insulation, high physical strength and stiffness, low weight, low moisture absorbance, flame resistance, low cost, and worldwide availability.